There are many areas of human behavior where we do not make the best possible choices due to the appeal of certain actions, even when they are not in our best interest. One example is diet: it is in our best interest to avoid obesity, but many people find it difficult to make the decisions that limit their calorie intake to the recommended level. Even those with diabetes whose health is significantly impacted by diet often find it hard to properly manage their calorie and carbohydrate intake during a day. There are many computer systems that generate advice, but they typically use only a small number of methods in their communication. One system relies on email; another on instant messages; a third on pop-up notifications. These systems do not generally vary their mode of communication nor do they learn from experience which modes are most successful.
On the other hand, when people communicate to each other, they use various techniques to be convincing. They may vary the modality of their advice to be effective and to avoid boredom, sometimes employing eMail, sometimes tweets, and sometimes instant messages. They may vary the calligraphy, sometimes employing boldface or capitalization to be more emphatic. They may vary whether others are copied on the message in order to increase pressure on the recipient. As a consequence, personal trainers have proven to be a very effective method for improving individual health; unfortunately, many persons who might benefit from a personal trainer cannot afford the associated cost.